Catalytic cracking of hydrocarbons with zeolite catalysts

ABSTRACT

Significant improvements in catalyst activity and selectivity are achieved in the catalytic cracking of hydrocarbons with catalysts of the zeolite type when the ratio of fresh catalyst addition to catalyst loss is maintained above 1.5 and the catalyst is heat treated at between 1,300* and 1,600* F. for between 5 minutes and 24 hours. The heat treatment is performed on either the fresh catalyst being added or on the combined mixture of fresh catalyst and equilibrium catalyst. Increases in Texaco D + L activity of between 1 and 10 may be achieved with concomitant increases in naphtha selectivity with naphtha yield at constant conversion being increased as much as 5 volume percent.

United States Patent [191 Youngblood 1 Dec. 18, 1973 CATALYTIC CRACKINGOF HYDROCARBQNS WITH ZEOLITE CATALYSTS [75] Inventor: Douglas J.Youngblood, Groves,

211 Appl. No.: 102,245

[52] US. Cl 208/120, 208/D1G. 2, 208/152, 208/164 [51] Int. Cl. B0lj9/20, COlb 33/28 .[58] Field of Search 208/120, 152

[56] References Cited UNITED STATES PATENTS 3,554,903 1/1971 Wilson208/164 3,135,683 6/1964 Mitchell 208/78 3,393,147 7/1968 Dwyer et a1.208/120 3,595,611 7/1971 McDaniel et a1. 23/111 3,149,924 9/1964 Cross23/288 3,553,104 1/1971 Stover et a1 208/120 3,518,051 6/1970 Maher eta1. 23/111 3,449,070 6/1969 McDaniel et a1. 23/111 3,384,602 5/1968Robinson 252/455 3,140,253 7/1964 Plank et a1 208/120 3,247,098 4/1966Kimberlin et a1. 208/120 3,325,397 6/1967 Plank et al 208/120 3,329,6287/1967 Gladrow et a1. 252/253 Primary ExaminerDe1bert E. Cantz AssistantExaminer-G. E. Schmitkons AttorneyThomas H. Whaley and Carl 6. Ries [57] ABSTRACT Significant improvements in catalyst activity andselectivity are achieved in the catalytic cracking of hydrocarbons withcatalysts of the zeolite type when the ratio of fresh catalyst additionto catalyst loss is maintained above 1.5 and the catalyst is heattreated at between 1,300 and 1,600 F. for between 5 minutes and 24hours. The heat treatment is performed on either the fresh catalystbeing added or on the combined mixture of fresh catalyst and'equilibriumcatalyst. 1ncreases in Texaco D L activity of between 1 and 10 may beachieved with concomitant increases in naphtha selectivity with naphthayield at constant conversion being increased as much as 5 volumepercent.

6 Claims, N0 Drawings BACKGROUND OF THE INVENTION This invention relatesto the catalytic cracking of hydrocarbons with catalysts of thecrystalline zeolite type. In particular, this invention relates toincreasing the catalyst activity and selectivity above that obtainedheretofore.

In the fluid catalytic cracking process, hydrocarbons are contacted withcatalysts of various types to effect transformation of the hydrocarbonsto desirable products such as gasoline, liquefied petroleum gas,alkylation feedstocks and middle distillate blending stocks. There is,however, a concomitant by-product formation of coke and gas which isoften undesirable. A particularly deleterious by-product of the processis coke which during the course of the hydrocarbon conversion isdeposited upon the catalyst. Since the coke deposition reduces thecatalyst activity and particularly the catalyst selectivity, catalyst iscontinuously withdrawn from the reactor and passed through aregeneration zone where it is contacted with an oxygen-containing gaseffecting combustion of substantial portions of the coke resulting inregeneration of the catalyst and returning it in large measure to itsformer activity. However, due to localized overheating within theregenerator repeated exposure of the catalyst to excessive hightemperature results in a gradual decline in the activity of theregenerated catalyst. Both the amorphous silicaalumina catalysts in useheretofore and the newer, more active'catalysts of the crystallinealuminosilicate type, which are finding wide application throughout thepetroleum industry, are sensitive to this localized overheating oftenencountered in fluid catalytic cracking regenerators. Exposure orcrystalline aluminosilicatecontaining catalysts in that portion of theregenerator where spent catalysts first contact air richest in oxygenresulting in hot spots in the order of 1650F. and higher results indeactivation of the zeolite catalysts through destruction of thecrystalline integrity of the aluminosilicate structure. However, eventhough only a small portion of the original zeolite content may remainin these catalysts after heat damage they still possess much highercatalytic activity than the amorphous silica-alumina catalysts.

Attrition of the catalytic cracking catalyst is a constant problem.While the cracking catalyst is transported between the regenerator andreactor vessels and circulated through the fluid beds in these vesselsit is subjected to severe abrading, resulting in fragmenting of thecatalyst pellet. Although the finely divided catalytic materialpossesses high activity it is not retained within the catalytic cackingunit but is lost through regenerator stack gases and fractionatorbottoms. Generally the loss of catalyst can amount to about 0.1 to 2.0weight percent of the catalyst inventory per day. About 75 percent ofthe catalyst losses normally occur through the regenerator stack gaseswith the remainder being lost through fractionator bottoms. Catalystdepletion by virtue of this attrition and loss must be alleviated byperiodic, and normally, daily, additions of fresh catalyst to maintainthe catalyst inventory at design level.

Although addition of fresh catalyst maintains catalyst inventory atrequired levels and prevents the equilibrium catalyst from decreasing inactivity, there is still a significant difference between the activityof the combined 'fresh catalyst and equilibrium catalyst and thatattainable by heat treating the fresh catalyst. A small increase inactivity, even an increase of 1.0 in Texaco D L activity, can result insubstantial and significant increase in the economic value of theproducts. In addition, an increase in activity is accompanied by asignificant increase in selectivity further enhancing the economicadvantage of activity increases. Therefore any modification to the fluidcatalytic cracking process, the catalyst or the operating conditionswhich enhances the activity and selectivity is highly desirable.

SUMMARY Broadly, this invention is directed to improvements in fiuidcatalytic cracking of hydrocarbons with catalysts of the crystallinezeolite type wherein the catalyst activity and selectivity aresubstantially increased by a combination of high fresh catalyst additionto equilibrium catalyst loss ratios and heat treating of the catalyst attemperatures above l300F. Specifically, the improvements are directed toadditions of fresh catalyst in a ratio of catalyst addition to catalystloss greater than 1.5 and heat treating either the fresh catalyst or allor a portion of the combined mixture of fresh and equilibrium catalystat temperatures between about 1300 and I600F. for 5 minutes to 24 hours.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Broadly, I have found thatsignificant improvements can be made in the catalytic cracking ofhydrocarbons with catalysts of the crystalline zeolite type where freshcatalyst is added in a ratio of fresh catalyst addition to equilibriumcatalyst loss greater than about 1.5 and subjecting the mixture ofequilibrium catalyst and fresh catalyst to a high temperature heattreatment. Alternately, the heat treatment may be confined to the freshcatalyst addition.

My invention contemplates improvements in the catalytic cracking ofhydrocarbons involving fresh catalyst additions and heat treatment ofthe catalyst. These improvements comprise:

a. adding fresh catalytic cracking catalyst of the crystalline zeolitetype to the inventory of equilibrium catalyst at a ratio of freshcatalyst addition to equilibrium catalyst loss greater than about 1.5,

b. withdrawing equilibrium catalyst from the catalyst inventory tomaintain the catalyst inventory at a substantially constant value, and

c. subjecting the mixture of equilibrium catalyst and fresh catalyst toa temperature of l300 to 1600F. for a period of between 5 minutes and 24hours.

In an alternate embodiment the heat treatment step is limited totreating the fresh catalyst rather than the mixture of equilibrium andfresh catalyst. Broadly, the improvements of this embodiment comprise:

a. subjecting fresh catalytic cracking catalyst of the crystallinezeolite type to a temperature of l300 to l600F. for a period of between5 minutes and 24 hours,

b. adding the treated catalyst from step (a) to the inventory ofequilibrium catalyst at a ratio of treated catalyst addition toequilibrium catalyst loss greater than about 1.5, and

c. withdrawing equilibrium catalyst from the catalyst inventory tomaintain the catalyst inventory at a substantially constant value.

This invention relates particularly to fluid catalytic cracking ofhydrocarbons employing catalytic cracking catalysts of the zeolite type.These catalysts comprise an active metal oxide, as exemplified bysilica-alumina or clay, and a large port crystalline alumino-silicate,customarily referred to as a zeolite. The zeolites employed in thesecracking catalysts possess ordered rigid three-dimensional structureshaving uniform pore diameters within the range of about 5 to about A.The crystalline zeolite catalysts to which these improvements aredirected comprise about 1 to 50 weight percent zeolite, about 10 to 50weight percent alumina with the balance being silica. Among thepreferred zeolites are those known as zeolite X, zeolite Y and mordenitewherein at least a substantial portion of the original alkali metal ionshave been replaced with such cations as hydrogen and/or metal orcombinations of metals such as barium, calcium, magnesium, manganese orrare earth metals, for example, cerium, lanthanum, neodymium,praeseodymium, samarium and yttrium.

In describing my invention, the terms fresh catalyst and equilibrium"catalysts have been used. By fresh catalyst, I mean a catalyst of thezeolite type as described hereinbefore which has been prepared but hasnot been utilized as a catalyst in a hydrocarbon conversion reaction.Thus, a catalyst as received from a catalyst manufacturer for use as acatalyst and which is added periodically to an operating catalyticcracking unit is an example of fresh" catalyst. After the fresh catalystis added to the catalyst inventory the properties of the catalystgradually undergo minor changes eventually reaching a substantiallyconstant value. For example, catalyst activity and selectivity generallyand gradually decline eventually reaching some equilibrium value. Thishas been explained by the fact that while carbonaceous material is beingremoved from the catalyst during regeneration it is subjectedoccasionally to excessively high temperatures in sections of theregenerator resulting in deterioration of the crystalline structure ofthe zeolite portion of the catalyst and modification of its catalyticproperties. After repeated regenerations and utilization as a crackingcatalyst the entire inventory of catalyst attains an equilibriumcondition regarding its catalytic cracking qualities. Thus, the catalystinventory of an operating catalytic cracking unit is composed of thisequilibrium catalyst.

Regarding the activity and selectivity of these catalysts, it is notunusual that fresh" zeolite catalyst has the following properties afterheat treatment: Texaco D L activity of between about 40 and 70 and aselectivity of between about 0.65 and 0.80. The Texaco D L activity testis described in 26 Petroleum Refiner No. 12,94 (I947). Selectivity," inthis instance, is defined as the volume percent of debutanized naphthadivided by the volume percent conversion of gas oil. After operation fora period of time during which exposure to regeneration temperatures andcontinuous use have reduced the catalytic properties of thealuminosilicate composition and during which periodic additions of freshcatalyst have been made to maintain catalyst inventory, the equilibriumcatalyst exhibits a Texaco D L activity of between and 40 and aselectivity of between about 0.64 and 0.75.

By the improvements of my invention which relate to a fluid catalyticcracking process, the activity and selectivity of equilibrium catalystcan be increased significantly over that obtained heretofore when thefresh catalyst additions are made in a ratio of fresh catalyst tocatalyst loss which is greater than about 1.5, preferably where theratio is between 2 and 2.5. When fresh catalyst additions are made,equilibrium catalyst must, of course, be removed to maintain thecatalyst inventory at a substantially constant value. In other words,the ratio of fresh catalyst addition to catalyst loss plus equilibriumcatalyst withdrawal must be 1.0 to maintain catalyst inventory at aconstant level.

Heat treatment of the catalyst is necessary to achieve the maximumbenefits of this process. Either the mixture of equilibrium catalyst andfresh catalyst may be heat treated or the heat treatment may be limitedto only the fresh catalyst addition. The heat treatment temperaturesshould be between 1300 and l600F. The heating should be conducted for atleast 5 minutes and although the catalyst may be exposed beneficially tothese temperatures for periods in excess of 200 hours a practical upperlimit for the heating period is about 24 hours. Preferably, the heattreatment is conducted between l400 and l550F. for a period of between15 and 200 minutes. Directionally the heat treatment should be conductedfor shorter periods of time when the higher temperature levels are used.The treatment is conducted in the absence of addes steam but air, fiuegas, nitrogen or other inert gases may be maintained in contact with thecatalyst during the heat treatment.

If only the fresh catalyst is being treated the treatment may beperformed continuously while the catalyst is being added or in batchesbefore the catalyst is added. When the mixture of catalyst is to be heattreated, a small slip stream or side stream of catalyst may be withdrawnat a point downstream from the fresh catalyst addition. This side streammay then be heat treated and returned at an appropriate place in theunit, preferably where the regenerated catalyst is being returned to thereactor.

By utilizing the process of this invention higher activity andselectivity levels are obtained than have been obtained heretofore. Thefollowing exemplifies the practice of this invention.

EXAMPLE I A series of tests was made with commercial szie fluidcatalytic cracking units using three different catalysts of thecrystalline zeolite type. These catalysts and their properties aredescribed in Table I below.

TABLE I Zeolite A B C Catalyst Zeolite type X X Y Matrix Silica- Silica-Silicaalumina alumina alumina Surface Area, m /g. 279 329 327 PoreVolume, cc/g 0.58 0.72 0.77 Zeolite content, wt. l 1 l8 3 Rare EarthContent, wt. 1.2 2.9 0.6 Activity of Fresh Catalyst, Texaco D L" 32 35SI Notes "Before heat treatment In a series of plant runs, the effect ofhigh catalyst addition to loss ratios and heat treatment of the catalyst6 was investigated. The mixture of equilibrium catalyst the inventory ofequilibrium catalyst at a ratio of and fresh catalyst was heat treatedat 1400F for 17 fresh catalyst addition to equilibrium catalyst losshours. The results obtained are presented in Table II greater than about1.5, below. Similar results are obtained where the heating b.withdrawing equilibrium catalyst from the catalyst time is less than 200minutes. 5 inventory to maintain the catalyst inventory at a From theresults of these tests, it is apparent that both substantially constantvalue, and activity and selectivity are substantially increased by a c.subjecting the mixture of equilibrium catalyst and combination of highaddition/loss ratios plus heat treatfresh catalyst to a temperature of1300 to I600F. ment of the mixtures of fresh and equilibrium catalyst.for a period of between 5 minutes and 24 hours. The catalysts from thehigher addition/loss ratio runs 2. A process according to claim 1wherein in step (a) generally had better activity and selectivity. theratio is between 2.0 and 2.5.

TABLE II Increase In Catalyst Before Heat Treatment After Heat TreatmentDB Naphtha Addition/ Yield 3 Catalyst Loss Ratio Activity SelectivityActivity Selectivity (Vol.

A 1.1 24 0.713 25 0.725 0.84 B 1.0 23 0.715 29 0.716 0.07 1.2 29 0.7190.768 3.43 2.6 33 0.683 36 0.758 5.25 C 1.4 26 0.698 29 0.704 0.42 2.339 0.710 43 0.732 1.54

Notes 1. Texaco D L Activity 2. Ratio of vol. debutanized (DB) naphthayield to vol. gas oil conversion 3. At a constant gas oil conversion of70 vol.

EXAMPLE II N v 3. A process according to claim 1 where in step (c) i ithe temperature is l400 to 1550F. for a period of be- To demonstrate theeffect of heat treating on the tween 15 and 200 minutes.

1 fresh catalyst, a series of four runs was conducted with 4. In thecatalytic cracking of hydrocarbons with a fresh catalyst B andequilibrium catalyst B. l 30 catalyst comprising an active metal oxideand crystal- A sample of equilibrium catalyst B from a refinery linezeolite, said catalyst having been rendered catalyticatalytic crackingunit was divided into four portions. cally active during its preparationby a process com- Activity and selectivity data were obtained on oneporprising calcining and/or steam treatment, wherein perition. The otherthree portions were blended with fresh odic additions of catalyst aremade to maintain catalyst catalyst B as received from the manufacturerand also 5 inventory which is gradually and continually depleted afterheat treatment. Activity and selectivity data were through attrition andloss, the improvement which obtained on these three blends. Results areshown in comprises:

Table III. Similar results are obtained where the heating a. subjectingfresh catalytic cracking catalyst comtime of Run 4 is less than 200minutes. prising an active metal oxide and a crystalline zeo- Thesetests show that heat treatment of only the fresh lite to a temperatureof 1300 to l600F. for a pecatalyst improves the activity and selectivityof the mixriod of between 5 minutes and 24 hours, ture of fresh andequilibrium catalyst. b. adding the treated catalyst from step (a) tothe in- TABLE III Run No.1 1 2 I 3 4 Catalyst composition (wt. FreshCatalyst B 25 wt. 25 wt. 25 wt.

Equilibrium Catalyst B 100%.. Heat treatment of fresh catalyst Activity30 Selectivity 0.658.. Increase in DB naphtha yield (vol.

NOTES:

Texaco D L.

2 Ratio of vol. percent debutanized (DB) naphtha yield to vol. percentgas oil conversion. *Increase over Run 2, at constant gas oil conversionof 70 vol. percent.

I clairnz ventory of equilibrium catalyst at a ratio of treated I. Inthe catalytic cracking of hydrocarbons with a catalyst addition toequilibrium Catalyst 1058 greater than about 1.5, and catalystcomprising an active metal oxide and a crystalline zeolite, saidcatalyst having been rendered catalytiwlthdrawmg equfhbflum catalyst mthe catalyst cally active during its preparation by a process inventoryto maintain the catalyst inventory at a prising calcining and/or steamtreatment, wherein peri- Substamany constfim valuei odic additions ofcatalyst are made to maintain catalyst A Process accordmg to clam 4where Step inventory which is gradually and continually depleted thetemperature is 14000 to 1550c? for 3 Period of through attrition andloss, the improvement which tween 15 and 200 utescomprises: 6. A processaccording to claim 4 where in step (b) a. adding fresh catalyticcracking catalyst comprising the ratio is between 2.0 and 2.5.

an active metal oxide and acrystalline zeolite to I

2. A process according to claim 1 wherein in step (a) the ratio isbetween 2.0 and 2.5.
 3. A process according to claim 1 where in step (c)the temperature is 1400* to 1550*F. for a period of between 15 and 200minutes.
 4. In the catalytic cracking of hydrocarbons with a catalystcomprising an active metal oxide and crystalline zeolite, said catalysthaving been rendered catalytically active during its preparation by aprocess comprising calcining and/or steam treatment, wherein periodicadditions of catalyst are made to maintain catalyst inventory which isgradually and continually depleted through attrition and loss, theimprovement which comprises: a. subjecting fresh catalytic crackingcatalyst comprising an active metal oxide and a crystalline zeolite to atemperature of 1300* to 1600*F. for a period of between 5 minutes and 24hours, b. adding the treated catalyst from step (a) to the inventory ofequilibrium catalyst at a ratio of treated catalyst addition toequilibrium catalyst loss greater than about 1.5, and c. withdrawingequilibrium catalyst from the catalyst inventory to maintain thecatalyst inventory at a substantially constant value.
 5. A processaccording to claim 4 where in step (a) the temperature is 1400* to1550*F. for a period of between 15 and 200 minutes.
 6. A processaccording to claim 4 where in step (b) the ratio is between 2.0 and 2.5.